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PubMed2001

Structural transitions in DNA driven by external force and torque.

Experiments on single DNA molecules have shown that abrupt transitions between states of different extensions can be driven by stretching and twisting. Here we show how a simple statistical-mechanical model can be used to globally fit experimental force-extension data of Léger et al. [Phys. Rev. Lett. 83, 1066 (1999)], over a wide range of DNA molecule twisting. We obtain the mean twists, extensions, and free energies of the five DNA states found experimentally. We also predict global force-torque and force-linking number phase diagrams for DNA. At zero force, the unwinding torque for zero-force structural transition from the double helix to an unwound structure is found to be approximately -2kBT, while the right-handed torque needed to drive DNA to a highly overwound state approximately 7kBT.

Base Pairing↗
PubMed2006

Recommended placement torque when tightening an orthodontic mini-implant.

To determine an adequate placement torque for obtaining a better success rate of mini-implants that are screwed into the buccal alveolar bone of the posterior region as an anchor for orthodontic treatment, implant placement torque (IPT) was measured. The subjects were 41 orthodontic patients (124 implants), with an average age of 24.9 years (SD 6.5 years), who had surgery to place titanium mini-implants. The peak value of IPT was measured using a torque screwdriver. The success rate of the mini-implant anchor for 124 implants was 85.5%. The mean IPT ranged from 7.2 to 13.5 N cm, depending on the location of the implants. There was a significant difference in the IPT between maxilla and mandible. The IPT in the mandible was, unexpectedly, significantly higher in the failure group than in the success group. Therefore, a large IPT should not be used always. According to our calculations of the risk ratio for failure, to raise the success rate of 1.6-mm diameter mini-implants, the recommended IPT is within the range from 5 to 10 N cm.

Adolescent↗
PubMedDate not supplied

Reflex torque response to movement of the spastic elbow: theoretical analyses and implications for quantification of spasticity.

A parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51 degrees +/- 10 degrees s.d. (n = 98) after the initial rise. This torque "plateau" was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles.

Adult↗
PubMed2002

Symmetry of discrete and oscillatory elbow movements: does it depend on torque that the agonist and antagonist muscle can exert?

The hypothesis that strength of active muscles affects the symmetry of the velocity profiles of voluntary movements was tested. In particular, it was assumed that the duration of acceleration and deceleration phases reflects the ability of the antagonistic muscles to exert torque in such a way that stronger muscle requires less time for action. Twelve subjects performed consecutive 50 flexions and extensions in blocks of either discrete or oscillatory movements. They were tested under high and moderate speed conditions, as well as within different ranges of elbow joint angles. The symmetry ratio (SR; acceleration time divided by deceleration time) was calculated in order to assess movement symmetry. The results demonstrated SR > 1 under most of the discrete and, particularly, oscillatory movement conditions. A velocity-associated increase in SR was recorded, while different ranges of elbow movements, assumed to provide different torques of the agonist and antagonist muscles, also provided different SR. The findings were generally in line with the predicted effects of movement conditions on muscle strength, particularly those related to elbow angle and elbow angular velocity. Deviations from the ideal movement symmetricity have usually been interpreted as either weakness of various motor control models and hypotheses, or as a sub-optimal control of movements in certain subject populations; the present study suggests an alternative interpretation based upon the ability of active muscles to exert torque

Adult↗
PubMed1999

Function of proline residues of MotA in torque generation by the flagellar motor of Escherichia coli.

Bacterial flagellar motors obtain energy for rotation from the membrane gradient of protons or, in some species, sodium ions. The molecular mechanism of flagellar rotation is not understood. MotA and MotB are integral membrane proteins that function in proton conduction and are believed to form the stator of the motor. Previous mutational studies identified two conserved proline residues in MotA (Pro 173 and Pro 222 in the protein from Escherichia coli) and a conserved aspartic acid residue in MotB (Asp 32) that are important for function. Asp 32 of MotB probably forms part of the proton path through the motor. To learn more about the roles of the conserved proline residues of MotA, we examined motor function in Pro 173 and Pro 222 mutants, making measurements of torque at high load, speed at low and intermediate loads, and solvent-isotope effects (D2O versus H2O). Proton conduction by wild-type and mutant MotA-MotB channels was also assayed, by a growth defect that occurs upon overexpression. Several different mutations of Pro 173 reduced the torque of the motor under high load, and a few prevented motor rotation but still allowed proton flow through the MotA-MotB channels. These and other properties of the mutants suggest that Pro 173 has a pivotal role in coupling proton flow to motor rotation and is positioned in the channel near Asp 32 of MotB. Replacements of Pro 222 abolished function in all assays and were strongly dominant. Certain Pro 222 mutant proteins prevented swimming almost completely when expressed at moderate levels in wild-type cells. This dominance might be caused by rotor-stator jamming, because it was weaker when FliG carried a mutation believed to increase rotor-stator clearance. We propose a mechanism for torque generation, in which specific functions are suggested for the proline residues of MotA and Asp32 of MotB.

Alleles↗
PubMedDate not supplied

Interference screw fixation strength of a quadrupled hamstring tendon graft is directly related to bone mineral density and insertion torque.

The purpose of this study was to determine whether bone mineral density of the host bone, measured using conventional dual photon absorptiometry techniques, and insertion torque can predict part of the ultimate failure strength of interference screw fixation of quadrupled hamstring tendon grafts. The semitendinosus and gracilis tendons were harvested from 10 human cadaveric knees, mean age 66.5 years (range, 53 to 81). The bone tunnel was sized within 0.5 mm of the graft. The graft was fixed with a biodegradable screw (7 x 25 mm for the femur, and 9 x 25 mm for the tibia) directly against the tendon and at the joint surfaces. Tibial fixation and femoral fixation were tested to failure using a materials testing system. Bone mineral density was measured in the metaphyseal region of the tibia and femur. The results of multiple regression analyses showed that both insertion torque and bone mineral density were related to the maximum load the graft withstood. These two variables explained 77.1% of the maximum load observed. We concluded that bone mineral density measurements of the host bone site are an important determinant of postoperative graft strength and thus have an important, but previously unrecognized, clinical role in establishing individual postsurgery rehabilitation protocols. Insertion torque in this study was a useful predictor of graft fixation strength.

Aged↗
PubMedDate not supplied

The effects of compressive load and knee joint torque on peak anterior cruciate ligament strains.

BACKGROUND: High graft strains incurred during rehabilitation after anterior cruciate ligament reconstruction may be minimized if an external compressive load is simultaneously applied to the joint during closed kinetic chain exercises. HYPOTHESES: Peak anterior cruciate ligament strains will 1). increase with an increase in resistance torque during an exercise that involves concentric contraction of the extensor mechanism, 2). decrease with an increase in resistance torque during an exercise that involves concentric contraction of the flexors, and 3). decrease when an external compressive load is applied to the knee during both exercises relative to the no external compressive load condition. STUDY DESIGN: Controlled laboratory study. METHODS: Strains in the anteromedial bundle were measured in 10 subjects with normal ligaments. Flexor and extensor exercises were performed against controlled resistance torques with and without a compressive load applied to the foot. RESULTS: An increase in resistance produced an increase in peak anterior cruciate ligament strain for the extensor exercise with no compressive load applied. During the flexor exercise without a compressive load, an increase in resistance produced a decrease in peak strains. During the extensor exercise, the peak anterior cruciate ligament strain was not reduced with the application of the external compressive force. CONCLUSIONS: Extensor and flexor exercises that incorporate an external compressive load do not shield the anterior cruciate ligament from strain. However, no additional increase in strain occurs with an increase in resistance when the external compressive load is applied. Thus, it may be possible to increase the activity of the quadriceps muscles without increasing the strain by applying a compressive load (as with closed kinetic chain exercises).

Adult↗
PubMed2000

Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient.

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(-)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously used for calculating the gliding performance of a peregrine. The accuracy with which drag coefficients measured on wingless bird bodies in a wind tunnel represent the C(D,par) of a living bird is unknown. Another method for determining C(D,par) selects values that improve the fit between speeds predicted by mathematical models and those observed in living birds. This method yields lower values for C(D,par) (0.05-0.07) than wind tunnel measurements, and the present study suggests a value of 0.1 for raptors as a compromise.

Air Movements↗
PubMed2003

Quadriceps femoris torque and EMG activity in seated versus supine position.

PURPOSE: To compare voluntary and electrically evoked knee extensor torque, surface electromyography (EMG), and activation level obtained under seated versus supine position, i.e., with shortened versus lengthened rectus femoris (RF) muscle. METHODS: The knee extensor torque obtained during maximal voluntary contractions (MVC) and after single and paired stimuli applied at rest was measured under seated (i.e., 90 degrees hip angle) and supine (i.e., 180 degrees hip angle) conditions. The associated EMG activity from biarticular RF and monoarticular vasti was also recorded, and activation level was estimated by means of the twitch interpolation technique. RESULTS: Knee extensor MVC was 10.6% higher in the seated compared with the supine position (P < 0.01). EMG normalized to the M-wave amplitude for respective muscles and for respective positions was significantly lower under supine conditions, and deficits averaged approximately 20% for vasti and approximately 41% for RF (P < 0.05). Similarly, activation level estimated in the supine position was approximately 4% lower than the seated counterpart. Relative MVC losses observed supinely were significantly correlated with the corresponding activation level deficits (P < 0.05). On the other hand, both single and paired stimuli resulted in higher torque amplitudes in the supine with respect to the seated position, and mean differences were comprised between 10% (single twitch, P < 0.05) and 20% (potentiated doublet, P < 0.001). RF M-wave amplitude recorded supinely was 19% higher than the seated counterpart (P < 0.01). CONCLUSION: The higher neural activation observed for the knee extensor muscles in the seated versus supine position, likely attributable to improved motor unit recruitment, may reflect a neurophysiological mechanism partly compensating the neuromuscular transmission-propagation impairment and/or mechanical disadvantage of shortened RF muscle.

Adult↗
PubMed1997

The effect of valve handwheel type, operating plane, and grasping posture on peak torque strength of young men and women.

An experiment was designed to assess the factors affecting the operation of valve handwheels. Forty volunteers (20 men and 20 women) participated in this study. A nested-factorial experimental design was employed. Handwheel type (smooth, curved, or knurled rim), operating plane (sagittal, frontal, or transverse plane), grasping posture (power or precision grasp), and operating direction (clockwise or counterclockwise) were found to have significant effects on the (maximum volitional torque exertion [MVTE]). A power grasp exerted more force than did a precision grasp. A smooth-rim handwheel oriented in the frontal plane resulted in the least MVTE. Counterclockwise torque exertion was significantly greater than clockwise torque exertion, but the difference was not very large. MVTE for women (7.9 Nm) was about 66% of that for men (12.0 Nm).

Adolescent↗
PubMed2003

Effect of static stretching of the biceps brachii on torque, electromyography, and mechanomyography during concentric isokinetic muscle actions.

The purpose of this study was to determine the effect of an acute static stretching bout of the biceps brachii on torque, electromyography (EMG), and mechanomyography (MMG) during concentric isokinetic muscle actions. Eighteen (men, n = 10; women, n = 8) adult subjects (M +/- SD age = 22.7 +/- 2.8 years; weight = 78.0 +/- 17.0 kg; height = 177.9 +/- 11.0 cm) performed maximal isokinetic (30 and 270 degrees.s(-1)) forearm flexion strength testing on 2 occasions while EMG and MMG were recorded. Subjects were randomly assigned to stretching (STR) or nonstretching (NSTR) protocols before strength testing. Two-way ANOVAs with repeated measures revealed significantly (p < or = 0.05) greater torque for NSTR (M +/- SEM = 36.9 +/- 3.3 N.m) vs. STR (35.2 +/- 3.3 N.m), significantly greater MMG amplitude for STR vs. NSTR for 30 degrees.s(-1) (STR = 93.5 +/- 14.4 mV; NSTR = 63.1 +/- 10.6 mV) and 270 degrees.s(-1) (STR = 207.6 +/- 35.6 mV; NSTR = 136.4 +/- 31.7 mV), and no difference in EMG amplitude. These results indicate that a greater ability to produce torque without prior stretching is related to the musculotendinous stiffness of the muscle rather than the number of motor units activated. This suggests that performing activities that reduce muscle stiffness (such as stretching), may be detrimental to performance.

Adult↗
PubMed2006

The rotor tip inside a bearing of a thermophilic F1-ATPase is dispensable for torque generation.

F(1)-ATPase is an ATP-driven rotary molecular motor in which the central gamma-subunit rotates inside a stator cylinder made of alpha(3)beta(3) subunits. To elucidate the role of rotor-stator interactions in torque generation, we truncated the gamma-subunit at its carboxyl terminus, which forms an alpha helix that penetrates deeply into the stator cylinder. We used an alpha(3)beta(3)gamma subcomplex of F(1)-ATPase derived from thermophilic Bacillus PS3 and expressed it in Escherichia coli. We could obtain purified subcomplexes in which 14, 17, or 21 amino-acid residues were deleted. The rotary characteristics of the truncated mutants, monitored by attaching a duplex of 0.49-microm beads to the gamma-subunit, did not differ greatly from those of the wild-type over the ATP concentrations of 20 nM-2 mM, the most conspicuous effect being approximately 50% reduction in torque and approximately 70% reduction in the rate of ATP binding upon deletion of 21 residues. The ATP hydrolysis activity estimated in bulk samples was more seriously affected. The 21-deletion mutant, in particular, was >10-fold less active, but this is likely due to instability of this subcomplex. For torque generation, though not for rapid catalysis, most of the rotor-stator contacts on the deeper half of the penetrating portion of the gamma-subunit are dispensable.

Bacillus↗
PubMed2000

Reverse torque testing and early loading failures: help or hindrance?

Reverse torque testing has been suggested to reduce the incidence of early loading failures during the first year of loading. However, the variables of bone density at stage II uncovery, the assessment of a small degree of implant rotation, and the effect of implant size and design have not been adequately evaluated. In addition, bone is weakest to shear forces, yet this is the primary force applied with reverse torque testing. This article reviews the benefits and disadvantages of reverse torque testing and suggests early crestal bone loss and failure of implants may be the result of this test, especially in less dense bone types. In addition, a nomenclature of implant failures is introduced to improve the correlation of information in the literature to the failure of implants in clinical practice.

Alveolar Bone Loss↗
PubMed2004

Effects of implant thread geometry on percentage of osseointegration and resistance to reverse torque in the tibia of rabbits.

BACKGROUND: Dental implant thread geometry has been proposed as a potential factor affecting implant stability and the percentage of osseointegration. Therefore, the aim of this prospective, randomized, parallel arm study was to evaluate the effects of dental implant thread design on the quality and percent of osseointegration and resistance to reverse torque in the tibia of rabbits. METHODS: Seventy-two custom-made, screw-shaped, commercially pure titanium implants (3.25 mm diameter x 7 mm length) were placed in the tibiae of 12 white New Zealand rabbits. Each tibia received three implants of varying thread shapes: one with a V-shaped, one with a reverse buttress, and one with a square thread design. The rabbits were sacrificed following an uneventful healing period of 12 weeks. Implants in the right tibiae underwent histologic and histomorphometric assessments of the bone-to-implant contact (BIC) and the radiographic density of surrounding bone, while implants in the left tibiae were used for reverse-torque testing. Differences between the three thread designs were examined using analysis of variance (ANOVA). RESULTS: Data showed that the square thread design implants had significantly more BIC and greater reverse-torque measurements compared to the V-shaped and reverse buttress thread designs, while no differences were found in radiographic bone density assessments. CONCLUSION: These results indicate that the square thread design may be more effective for use in endosseous dental implant systems.

Analysis of Variance↗
PubMed2001

Anterior tibial translation during different isokinetic quadriceps torque in anterior cruciate ligament deficient and nonimpaired individuals.

STUDY DESIGN: Factorial quasi-experimental design. OBJECTIVES: To quantify the effect of different levels of isokinetic concentric and eccentric knee extensor torques on the anterior tibial translation in subjects with anterior cruciate ligament (ACL) deficiency. Electromyogram (EMG) activity of 4 leg muscles was recorded in order to detect any co-activation of extensors and flexors. BACKGROUND: The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. In order to construct a rehabilitation program after that injury, it is important to understand the in vivo relationships between muscle force and tibial translation. METHODS AND MEASURES: Twelve patients with unilateral ACL injury and 11 uninjured volunteers performed 36 repetitions of a quadriceps contraction at different isokinetic concentric and eccentric torque levels, on a KinCom machine (60 degrees x s(-1)), with simultaneous recordings of tibial translation (CA-4000) and EMG activity from quadriceps and hamstrings muscles. Tibial translations and EMG levels were normalized to the maximum of each subject. RESULTS: The individual anterior tibial translation increased with increased quadriceps torque in a similar manner in both quadriceps contraction modes in all legs tested. During concentric mode, translation was similar in all groups, but during eccentric mode, the mean translation was 38% larger in the ACL injured knees. No quadriceps-hamstrings co-activation occurred in any test or group. CONCLUSIONS: An ACL deficient knee can limit the translation within a normal space during concentric muscle activity but not during eccentric activity. That limitation depends on other mechanisms than hamstrings co-activation.

Adolescent↗
PubMed2006

Wrist extensor torque production and discomfort associated with low-frequency and burst-modulated kilohertz-frequency currents.

BACKGROUND AND PURPOSE: A randomized controlled trial to compare 2 forms of monophasic pulsed currents with 2 forms of burst-modulated, kilohertz-frequency alternating current ("Russian current" and "Aussie current") was conducted to establish whether different amounts of wrist extensor torque were produced and whether discomfort varied with stimulus type. SUBJECTS: The 32 subjects were adults who were healthy and were drawn from a population of staff and students at La Trobe University. METHODS: Each subject received all 4 currents. Maximal electrically induced torque (MEIT) of the wrist extensors was measured for each stimulus type. Relative discomfort of stimulation also was assessed. RESULTS: Russian current elicited lower mean torque than those elicited by Aussie current and monophasic pulsed currents. The Russian and Aussie currents elicited significantly less discomfort than the 2 monophasic pulsed currents. DISCUSSION AND CONCLUSION: When force production and relative discomfort were jointly used as the criteria, Aussie current was found to be more effective than either of the monophasic pulsed currents or Russian current stimulation.

Adult↗
PubMed2000

Effects of squat lift training and free weight muscle training on maximum lifting load and isolinetic peak torque of young adults without impairments.

BACKGROUND AND PURPOSE: Manual lifting is a frequent cause of back injury, and there is no evidence as to which training mode can provide the best training effect for lifting performance and muscle force. The purpose of this study was to examine the effects of a squat lift training and a free weight muscle training program on the maximum lifting load and isokinetic peak torque in subjects without known neuromuscular or musculoskeletal impairments. SUBJECTS: Thirty-six adults (20 male, 16 female) without known neuromuscular or musculoskeletal impairments participated. The subjects' mean age was 21.25 years (SD=1.16, range=20-24). METHODS: Subjects were divided into 3 groups. Subjects in group 1 (n=12) performed squat lift training. Subjects in group 2 (n=12) participated in free weight resistance training of their shoulder abductors, elbow flexors, knee extensors and trunk extensors. Subjects in group 3 (n=12) served as controls. The maximum lifting load and isokinetic peak torques of the trunk extensors, knee extensors, elbow flexors, and shoulder abductors of each subject were measured before and after the study. Training was conducted on alternate days for 4 weeks, with an initial load of 80% of each subject's maximum capacity and with the load increased by 5% weekly. RESULTS: All groups were comparable for all measured variables before the study. After 4 weeks, subjects in groups 1 and 2 demonstrated more improvement in maximum lifting load and isokinetic peak torque of the back extensors compared with the subjects in group 3, but the 2 training groups were not different. CONCLUSION AND DISCUSSION: The findings demonstrate that both squat lift and free weight resistance training are equally effective in improving the lifting load and isokinetic back extension performance of individuals without impairments.

Adult↗
PubMed1997

[The developement of a new torque experiment device for biomaterials].

This paper introduces a biomaterial torque experiment apparatus which consists of AST486 computer, photodiode array, code device interface circuit, and magnetoelectric motional coil structure. According to experimental conditions, the computer sends out signal to the coil which under the magnetic field is activated to produce a series of desired torque and bring the sample to deflect. Angular displacement is measured by photodiode array and code device system. The whole system has good dynamics and high precision and could finish a series of torque experiment for biomaterials, and AST486 computer can automatically conduct signals analyzing and data processing.

Biocompatible Materials↗